FIG. 4.

LTR structure of acquired proviruses in wild-type and mutant MMTV-induced mammary tumors (MT) and thymic lymphomas (TL). (A) Southern blotting of tumor DNA using the full-length MMTV LTR probe. (B) Southern blotting of tumor DNA with the MMTV NRE probe (StuI-to-AflII fragment of the MMTV LTR). Genomic DNA was digested with PstI, separated on 0.8% agarose gels, transferred to nitrocellulose, and hybridized as previously described (9). Southern blotting of genomic DNA from an uninfected BALB/cJ mouse liver (LI) was used to distinguish the bands originating from the three endogenous Mtvs in the BALB/cJ strain. White asterisks (lanes 5, 7, 10, 11, and 13) indicate the LTR fragments of predominant acquired proviruses in virus-induced tumors.